Silicon and zirconium based lacquer, its use as a substrate coating and substrates thus obtained

ABSTRACT

The present invention relates to a lacquer obtained by the process comprising the steps of: (i) precondensation of: a) 1 to 10 mol % of at least one zirconium compound of the formula ZrR 4  ; b) 20 to 94 mol % of at least one organic silane of the formula R&#34; m  (R&#39;&#34;Y) n  SiX.sub.(4-m-n) ; c) 5 to 30 mol % of at least one organic silane of the formula R&#34; p  SiX 4-p  ; d) optionally 0 to 10 mol % of at least one low-volatility metal oxide; and (ii) hydrolysis condensation of the precondensate of step (i) in the presence of 0 to 50% of the stoichiometric amount of water. The invention also relates to a process for the obtention of a coating on substrate which comprises the steps of applying the lacquer and curing same. The invention also relates to the thus-coated substrates.

The present invention relates to a novel silicon and zirconium basedlacquer, its use as a substrate coating and the thus-obtainedsubstrates.

Hitherto, studies and efforts have been made to obtain lacquers endowedwith improved technical properties, to be used as coating for substrateswhich are typically used in extremely harsh environments. Examples ofcoatings which allow the coated substrates to be used in said harshenvironments are coatings with properties such as: anti-contamination,anti-scratch, heat-resistance and refractory properties, low moisturepermeability, resistance to chemicals, insulation properties,oxygen-barrier, high bulk resistivity, low friction coefficient, highadhesion to the substrates and the like.

The fields wherein said coatings may be used are varied and numerous.One can cite, as illustrative, those fields wherein the coatings provideprotection for active and passive electrical, electronic, opticalcomponents and assemblies thereof against environmental stresses.

During the past years, research in the field of micro-electronics hasbeen directed to higher productivity and devices miniaturisation. Thus,the use of surface-mounted devices (SMD), rendering high-speed componentplacement possible, has lead to significant gain in productivity, thesoldering of such surface mounted devices (SMD) on the printed circuitsnow being carried out on the face(s) of the circuit where the devicesare lodged. The two soldering processes currently used are wavesoldering and reflow soldering. The first of these two processes, theso-called wave soldering process, comprises the step of bringing theprinted circuit bearing the SMDs adhered thereon into contact with astationary wave formed in a bath of molten solder, the parameters oftemperature and time being respectively about 260° C. and about 10 s forconventional tin/lead solder, given that the operating conditions varyas a function of the solder employed. The second process, so-calledfellow soldering, comprises the step of applying solder in the solidstate at the contact pins of the SMD adhered on the printed circuitboard followed by heating, using IR radiation or vapor phase transfer,of the foregoing assembly at a temperature of about 220° C. for a periodof time of about 30 secs. The component and the substrate are thussubmitted to somewhat drastic thermal conditions, but they must ofcourse retain their properties, especially electronic properties, i.e.the shift due to the thermal treatment should be less than a fewpercent, typically less than 3%.

Concurrently, efforts have been directed to miniaturise the componentsthemselves and new components such as new capacitors, have beendeveloped. These new capacitors known as thin-film capacitors areobtained by laminating thin layers of metal, e.g. aluminium, and thinlayers of a bulk dielectric material, the electrode pins of this SMDbeing obtained by deposition of metal, e.g. aluminium. Good andpromising results have been obtained with such capacitors, obtained fromfilms made of polyester e.g. polyethylene terephtalate (PET) orpolyethylene naphtalate (PEN) and which have been metallized. An exampleof a manufacturing process for said new capacitors is the process knownas Interleaf®. Processes for preparing thin-film capacitors are forexample described in the following U.S. Pat. Nos.: 4,741,876, 4,744,462,4,533,813, 4,535,381, 4,531,268, 4,534,488, and 4,531,340.

However, these new components, such as the above thin-film capacitors,suffer from certain drawbacks. One is that polyester foils are known toabsorb water. This water will cause corrosion and erosion of aluminiumelectrodes (the metal foils), and also a capacitance shift which occursdue to moisture content changes, meaning that during the above-mentionedsoldering processes the rapid evaporation of water will tend to causedelamination.

These problems connected with water are cumulated with the lowmelting-point of the polyester. Therefore, the use of thin filmcapacitors as microelectronic SMDs which can withstand the solderingprocesses requires encapsulation of these thin films. The encapsulatingcasing has to be endowed with insulation properties in order to protectthe SMD. But now the benefit gained thanks to the miniaturisation of thecapacitors is lost, due to the bulkiness of the insulating casing.

An alternative has thus been proposed in order to avoid the use of saidinsulating casing. It is based on the coating of the component SMD e.g.the capacitor, with a material which acts as a barrier and thus preventdegradation of the SMD. But the properties required are multiple. Majorproperties, among others, are, in the case of the above-mentioned SMDsuch as a thin film capacitor: efficiency at low thickness, highadhesion on the substrate such as aluminium and polyester, lowpermeability to moisture, thermal properties sufficient to withstanddrastic soldering conditions, electrical properties such as high surfaceand bulk resistance and high breakdown voltage, chemical properties likesolvents and soaps resistance, easy application on the substrates,absence of harmfulness to the environment and the like. Variousmaterials have been provided, such as polyvinyl chloride (PVC), highdensity polyethylene (HDPE) and the like, as a coating for SMDs andothers, but the results thus obtained are not satisfying. Thesematerials, known as water barrier materials, are not adherent to thesubstrate, made from, e.g. polyester, silicon, ceramic, metal, and thelike and are not able to withstand high temperatures.

Similar and other problems arise with a wide variety of SMDs, as well aswith optical devices, printed circuit boards, and the like. Examples ofsubstrates contemplated within the scope of the present invention are,by way of illustration: resistors, integrated circuits, opticalwaveguides and switches, multichip modules (MCMs), Si-wafers, printedcircuit boards (PCBs) such as PCBs based on FR-4 laminates or Al₂ O₃-ceramic boards with Cu- and Au-conductor lines, and hybrid circuits.

Also, enhanced integration, faster signal transmission, similarly to thereduced size of SMD, requires new patternable materials. The potentialof new generations of RAM and ROM chips, especially processors, cannotbe fully used without enhanced integration and multilayer technology.Therefore microelectronics requires tailormade materials and newtechniques for interconnection. Multilayer technology demandspatternable dielectric materials with specific properties, such as: highbreakdown voltage, low permittivity constant, high bulk resistance, highcorrosion resistance, high adhesion to various types of substrates, andthe like. Such materials, endowed with the afore-mentioned properties,applied as a coating and further processed, would open up newdevelopments for very large system integration techniques (VLSI).

The foregoing examples show a need for a variety of coatings endowedwith improved properties. But, a unique coating for use as a coating innearly all cases would be most advantageous. This would allow, forexample, one-step processing of the PCBs with all SMDs arranged thereon.Attempts have been made to attain such a coating with numerousproperties, but the results obtained so far are not promising.

EP-A-0171493 describes a lacquer which is scratch-resistant. Thislacquer is obtained by polymerizing: a) a zirconium compound, ZrR₄, b) asilane of the formula R'_(m) (R"Y)_(n) SiX.sub.(4-m-n) wherein Y is apolymerizable group, and c) a low-volatility oxide. There is no mentionof the specific lacquer according to the present invention, neither ofthe use thereof as a coating for electronic or optical devices.

EP-A-0078548 describes a polycondensate for use as lens material,especially for contact lenses. This polycondensate is obtained bypolymerizing: a) a zirconium compound, ZrR₄, b) a silane of the formulaR'_(m) (R"Y)_(n) SiX.sub.(4-m-n) wherein Y is a polymerizable group, c)a silane of the formula R_(p) ^(") SiX_(4-p) and d) a low-volatilityoxide. There is no mention of the specific lacquer according to thepresent invention, neither of the use thereof as a coating forelectronic or optical devices.

The aim of the invention is to provide said "universal" coating, thanksto the application of a novel lacquer.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the relative capacitance shifts on coated and uncoated 2 μmthin-film PEN-capacitors (100 nf) in a 90° C., 100% RH life test.

Thus, the present invention provides a lacquer obtained by the processcomprising the steps of carrying out:

(i) precondensation of:

a) 1 to 10 mol % of at least one zirconium compound of formula I:

    ZrR.sub.4                                                  (I)

wherein:

R is halogen, hydroxy, alkoxy, acyloxy, or chelated ligand;

b) 20 to 94 mol % of at least one organic silane of the formula II:

    R".sub.m (R"'Y).sub.n SiX.sub.(4-m-n)                      (II)

wherein

R" is alkyl, alkenyl, aryl, alkylaryl, arylalkyl, alkenylaryl,arylalkenyl,

R"' is alkylene, alkenylene, arylene, alkylarylene, arylalkylene,alkenylarylene, arylalkenylene, R" and R"' being optionally interruptedby oxygen, sulfur, or --NH--,

X is hydrogen, halogen, hydroxy, alkoxy, acyloxy, -NR₂ 'where R' is H oralkyl,

Y is a polymerizable group,

m and n are integers from 0 to 3;

where m+n is from 1 to 3; and

c) 5 to 30 mol % of at least one organic silane of the formula III:

    R.sub.p.sup." SiX.sub.4-p                                  (III)

wherein R" and X have the above meaning, and p is 1, 2 or 3; andoptionally

d) 0 to 10 mol % of at least one low-volatility metal oxide, soluble inthe reaction medium, of an element of main groups Ia to Va or sub-groupsIVb or Vb, or a compound of one of these elements, soluble in thereaction medium, forming a low-volatility oxide;

preferably in the absence of water, optionally in the presence of anorganic solvent at a temperature comprised between 10° and 80° C. for aperiod of time comprised between 0.5 and 72 hours; and

(ii) condensation of the precondensate of step (i) without water or withup to 50% of the stoichiometric amount of water, at a temperaturecomprised between 20° and 90 ° C. for a period of time comprised between0.5 and 72 hours.

Preferably, component a) of formula I represents from 2 to 6 mol%, thecomponent b) of formula II represents 69 to 83 mol%, the component c) offormula III represents 15 to 25 mol%, and the component d) is absent.

In the above formulae I, II and III, the groups R, R', R", X or Y whichmay be present several times in one or more compound(s), may have thesame meaning or different meanings. Thus, for example, the group X informulae II and III may be methoxy in both formulae or methoxy informula II and hydroxy in formula III. Also, the group R in formula Imay have from four distinct meanings to one unique meaning.

The term "alkyl", as used herein, is intended to mean, but is notlimited to, saturated, straight, branched or cyclic groups having from 1to 20, preferably from 1 to 10 carbon atoms, more preferably from 1 to6; the most preferred groups are lower alkyl groups containing 1 to 4carbon atoms. Examples of such groups are, by way of illustration:methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl,isobutyl, n-pentyl, n-hexyl and cyclohexyl.

The term "aryl", as used herein, is intended to mean aromatic groupshaving from 6 to 25, preferably 6 to 14, and most preferably 6 to 10carbon atoms. Examples are phenyl and naphthyl; phenyl being thepreferred aryl group.

The term "alkenyl", as used herein, is intended to mean mono- orpoly-unsaturated, straight, branched or cyclic group having from 2 to20, preferably 2 to 10, more preferably 2 to 6 carbon atoms. Examples ofsuch groups are: allyl, 2-butenyl and vinyl.

The groups alkylaryl, arylalkyl, alkenylaryl, arylalkenyl, alkylene,alkenylene, arylene, alkylene-arylene, arylene-alkylene,alkenylene-arylene, arylene-alkenylene, alkoxy, acyloxy, alkylamino,dialkylamino, amides, alkylcarbonyles, alkoxycarbonyles and the like arederived from the above mentioned alkyl, aryl and alkenyl groups,according to the nomenclature well-known to the man skilled in the art.Examples of such groups are: methoxy, epoxy, n- and i-propoxy, n-sec-and tert-butoxy, isobutoxy, β-methoxy-ethoxy, acetyloxy, propionyloxy,monomethylamino, monoethylamino, dimethylamino, diethylamino, ethylene,propylene, butylene, phenylene, toluylene, benzyl, styryl,methylcarbonyl, ethylcarbonyl, methoxycarbonyl and ethoxycarbonyl.

The above groups may be substituted by one or more usually employedsubstituents, such as halogen, lower alkyl, hydroxy, nitro, amino, andthe like. The term "halogen" as used herein intends to mean fluorine,chlorine, or bromine, chlorine being preferred.

The zirconium compound a) of the formula I is:

    ZrR.sub.4                                                  (I)

wherein:

R is halogen, hydroxy, alkoxy, acyloxy or chelated ligand;

and is also referred to as the "inorganic network former".

Examples of inorganic network former zirconium compounds are, by way ofillustration: ZrCl₄, Zr(O--C₃ H₇)₄, Zr(O--C₄ H₉)₄, Zr(acetylacetonato)₂(O--C₃ H₇)₄, Zr(acetylacetonato)₄, Zr compounds with chelated ligands,preferably coordinated by oxygen or nitrogen. The preferred group isZr(O--isoC₃ H₇)₄, i.e. tetraisopropoxy zirconate, referred tohereinafter as Zr in the formulae for the lacquer.

The silane b) of the formula II is:

    R".sub.m (R"'Y).sub.n SiX.sub.(4-m-n)                      (II)

wherein:

R" is alkyl, alkenyl, aryl, alkylaryl, arylalkyl, alkenylaryl,arylalkenyl, preferably methyl;

R"' is alkylene, alkenylene, arylene, alkyl-arylene, aryl-alkylene,alkenyl-arylene, aryl-alkenylene, preferably C₁₋₄ alkylene R" and R"'being optionally interrupted by oxygen, sulfur, or --NH--,

X is hydrogen, halogen, hydroxy, alkoxy, acyloxy, --NR₂ ' where R' is Hor alkyl, preferably C₁₋₄ alkoxy

Y is a polymerizable group, preferably methacryloxy, acryloxy, epoxy,vinyl, allyl;

m and n are integers from 0 to 3, preferably 0 and 1 respectively;

m+n is from 1 to 3;

and is also referred to as the "organic network former". The bridginggroup R"' may optionally be interrupted by heteroatoms, such as oxygen,sulfur, and nitrogen, as --NH--. Thus, 2 to 10 recurring units, such aspolyethers, can be advantageously obtained.

Examples of a functional organic network former are: ##STR1##Preferably, component b) of formula II is (R"'Y)SiX₃, wherein R"' is aC₁₋₄ alkylene, Y is acryloxy, methacryloxy, glycidyloxy, vinyl, allyl,epoxycyclohexyl, and X is C₁₋₄ alkoxy.

Most preferred groups are:

3-glycidyloxypropyltrimethoxysilane and3-methacryloxypropyl-trimethoxysilane, respectively abbreviated as glymo(G) and memo (M) hereinafter.

The silane c) of the formula III is:

    R.sub.p.sup." SiX.sub.4-p

wherein R", X and p have the above meaning, and is also referred to asthe "network modifier".

Examples are, by way of illustration:

CH₃ --Si--Cl₃, CH₃ --Si--(OC₂ H₅)₃, C₂ H₅ --Si--Cl₃,

C₂ H₅ --Si--(OC₂ H₅)₃, CH₂ ═CH--Si--(OC₂ H₅)₃,

CH₂ ═CH--Si--(OC₂ H₄ OCH₃)₃, CH₂ ═CH--Si--(OOCCH₃)₃,

(CH₃)₂ --Si--Cl₂, (CH₃)₂ --Si-(OC₂ H₅)₂, (C₂ H₅)₂ (Si--(OC₂ H₅)₂,

(CH₃)(CH₂ ═CH)--Si--Cl₂, (CH₃)₃ --Si--Cl (C₂ H₅)₃ --Si--Cl,

(t--C₄ H₉)(CH₃)₂ --Si--Cl, (CH₃)₂ (CH₂ ═CH--CH₂)--Si--Cl,

(CH₃)₂ --Si(OCH₃)₂, (CH₃)₂ --Si--(OCH₃)₂, (C₆ H₅)₂ --Si--Cl₂,

(C₆ H₅)₂ --Si--(OC₂ H₅)₂, CH₂ ═CH--Si--Cl₃, CH₂ ═CH--CH₂ --Si--(OC₂H₅)₃,

CH₂ ═CH--CH₂ --Si--(CH₃ COO)₃, (i--C₃ H₇)₃ --Si--OH and

(C₆ H₅)₂ --Si--(OH)₂.

Preferably, p is 2; R" is aryl and X is hydroxy or C₁₋₄ alkoxy.

The most preferred network modifier is (C₆ H₅)₂ --Si--(OH)₂,diphenylsilanediol, hereinafter abbreviated as P2.

The silanes and the zirconium compounds are either commerciallyavailable, or are readily prepared according to methods well-known bypeople skilled in the art; see for example W. Noll "Chemie undTechnologie der Silicone", Verlag Chemie GmbH, Weinheim, Bergstrasse(1968). Care should be taken that the silanes and the zirconates arepure; trace amounts of electrolytes such as Cl, B, Ca, Ti, and the likeadversely affect the reaction conditions and the properties of thethus-obtained lacquer.

In lieu of the monomers (a), (b) or (c), their respective oligomers mayalso be used. These oligomers are soluble in the reaction medium andthey are partial precondensates. These partial precondensates, or linearor cyclic polyorganosiloxanes -polyorganozirconates- have a lowmolecular weight, the condensation rate ranging from 2 to 100.

As the optional component (d), one can use low-volatility oxides,soluble in the reaction medium of an element of main groups Ia to Va orsub-groups IVb or Vb of the Periodic Table, or alternatively onecompound of one of these elements, soluble in the reaction medium,forming a low volatility oxide as previously described under thereaction conditions. Preferably, component (d) is obtained starting fromone of the following elements: Na, K, Mg, Ca, B, Al, Sn, Pb, P, As, Sband/or V; more preferred are Na, K, Ca, Mg, B, Al, Sn, As and P.

Among the low-volatility oxides, the preferred oxides are Na₂ O, K₂ O,CaO, SnO₂, As₂ O₃, P₂ O₅, B₂ O₃. B₂ O₃ is most preferred.

The compounds soluble in the reaction medium and forming theabove-mentioned low-volatility oxides are numerous. Mineral acids aresuitable, such as phosphonic acid, boric acid, as well as their esters,halogenides and salts. Also suitable are the hydroxides such as NaOH,KOH or Ca(OH)₂, halogenides such as SnCl₄ and PCl₅, and alcoholates suchas NaOR, KOR, Ca(OR)₂ or Al(OR)₃, the group R being derived from a loweralcohol such as methanol, ethanol, propanol and butanol. Startingcompounds which may optionally be used are the corresponding salts withvolatile acids, such as acetates, basic acetates, basic lead acetate andformiate.

In order to achieve the condensation leading to the heteropolycondensateforming the lacquer, the starting components a), b), c) and optionallyd), according to the desired amounts and ratios are firstly subjected toa precondensation step. This step is carried out preferably in absenceof water, optionally in the presence of an organic solvent, which may beinert under the reaction conditions. This organic solvent is, forexample, an alcohol, such as methanol, ethanol, propanol, butanol, anether, such as dimethoxyethane, an ester such as dimethylglycolacetate,or a ketone such as acetone or methylethylketone. Preferably, theprecondensation step is carried out without any external organicsolvent. This step is preferably carried out without external additionof water, the water which is present in the reaction medium is resultingfrom the condensation reaction of the OH-groups of diphenylsilanediol(component c), and also of the OH-groups with alkoxy-groups. This watermay start subsequent condensation of the other components, but to aminor extent.

The precondensation may be carried out in the presence of a catalyst,for example compounds generating proton H⁺ or hydroxyl ions OH⁻ as wellas amines. Examples of H⁺ -generating compounds are organic or mineralacids, such as hydrochloric acid, sulfuric acid, phosphoric acid, aceticacid and formic acid. Example of OH⁻ -generating compounds and of aminesare amonia, hydroxides of alkaline or alkaline-earth metal, e.g. sodium,potassium and calcium hydroxide, and amines which are soluble in thereaction medium, e.g. lower alkylamines and lower alkanolamines.Preferred catalysts are formic acid and ammonia. The total amount ofcatalyst may range up to 3 mol/l, for example.

The precondensation step is usually carried out at a temperature rangingfrom 10° to 80° C., preferably from 15° to 50° C. The period of timeneeded for completion of the precondensation step is comprised between0,5 and 72 h, preferably between 1 and 48 h. When solvents are used, thesame ranges usually apply, including the boiling temperature of thesolvent. However, the reaction is preferably carried out at roomtemperature. The solvent may be removed from the precondensation mediumat the end of the reaction.

Optionally, the precondensation may be carried out by firstprecondensation of one or more of the starting components, or of part ofone, several or all starting components, and by subsequently adding theremaining component(s) or part thereof and thus finally carrying out theprocess of precondensation, or alternatively the process of the furthercondensation.

The precondensation is carried out up to a degree of advancement suchthat the precondensate still shows a liquid consistency.

The subsequent condensation (ii) of the precondensate, optionally as asolution free of solvent, is carried out in in the presence of 0 to 50%of the stoichiometric amount of water. The stoichiometry, used in thepresent specification, is calculated based on the starting materialsinitially used. Preferably, the amount of water is comprised between 0and 25% of the stoichiometric amount. According to a preferredembodiment of the present invention, the hydrolysis of the hydrolysablegroups takes place in an anhydrous medium, i.e. the condensation iscarried out without added water.

Condensation step (ii) may be carried out in the presence of a catalyst,of the type of the one mentioned hereinabove. Preferred catalysts forthe condensation (ii) are formic acid and ammonia. The total amount ofcatalyst may range up to 5 mol/l, for example. During said condensation,one of the previously mentioned organic solvent may be present, eitherat the beginning of said condensation (ii) if not removed at thecompletion of the precondensation (i), or it may be added during saidcondensation. If a solvent is used during the condensation step it maybe removed using vacuum.

The condensation (ii) is carried out at a temperature comprised between20° and 90° C., preferably between 25° and 70° C., and for a period oftime comprised between 0.5 and 72 hours, preferably between 2 and 48 h.The reaction parameters, particularly the reaction time, are adjusted asa function of the nature of the starting materials, the reactionconditions of the precondensation, the temperature of the condensation,and the desired viscosity of the lacquer to be obtained. Typically, thecondensation is continued so as to obtain the desired inherent viscosityfor the lacquer. Preferably, said inherent viscosity is comprisedbetween 5 and 1000 mm² /s. This viscosity is chosen so as to allow thelacquer to be easily processed, i.e. to be easily applied to the subjectsubstrate. The viscosity is measured according to known methods, such ascapillary viscosimetry.

The lacquer may be used as such for the coating, or it may containadditional additives. These additives are usual, and include but are notlimited to: organic diluents, antisagging adjuvant, pigments, dyes,UV-stabilisant, viscosity-regulator, anti-oxidant, fillers. Preferably,the lacquer contains fillers, such as: clay, calcinated clay, Aerosil®,α-calcite, glass fibers, glass flakes, talc, and the like. The fillermay represent from 1 to 70 weight %, based on the weight of the lacquer.Preferred fillers are Luzenac talc and glass fibers/flakes, which may beincorporated in the lacquer prior to coating or sprinkled thereon oncecoated.

There is no specific requirement as to when the lacquer has to beprocessed, since the time limit is about 15 years after completion ofthe condensation reaction; preferably it is applied within 200 daysafter the end of the condensation. This requirement is due to thevariation of viscosity. Alternatively, the lacquer may be obtainedstep-wise, i.e. by carrying out the precondensation and the condensationat two different times; in this case, care should be taken to store theprecondensate in a water-free environment and at a low temperature sothat the condensation reaction cannot start.

According to another embodiment, the lacquer can be stored free ofsolvent, the solvent being removed by, e.g., distillation. If necessary,a solvent and/or a reactive diluent can be added before application toadjust the viscosity. The solvent is the usual solvent (e.g. propanol,butoxyethanol, propoxyacetate). The reactive diluent is, e.g., styreneoxide, phenyl glycidyl ether, neopentylglycol diglycidyl ether, and isincorporated with advantage into the organic network during the curingprocess.

Another object of the present invention is a process for the obtentionof a coating on a substrate which comprises the steps of applying alacquer according to the present invention on said substrate and curingsaid lacquer.

The lacquer is applied according to known methods. Examples of saidusual methods for applying a lacquer are: brushing, printing,screen-printing, dip-coating followed by spinning-off, soaking, sprayingand the like. The method for applying the lacquer is determined based onthe viscosity of the lacquer and the substrate to be coated, oralternatively the viscosity of the lacquer may be adjusted in order tobe processed in the specific process used in the plant. Also, thecomponent may not need to be coated on all its sides: for example, acubic substrate which needs to be coated on two sides only can be coatedon these sides only using the method which is best suited; this is thecase for SMDs such as thin-film capacitors which present two mainoxidisable faces. The lacquer thus applied is then cured in order togain its remarkable properties.

The step subsequent to the condensation is the curing of the condensateof step (ii). This curing is the polymerization of the polymerizablegroup Y of the organic network former b). This polymerization may be aradical photopolymerization, a thermal and/or hardener polymerization.

The curing may be initiated either by thermal treatment and/or byhardeners, i.e. curing agents. The hardeners may be used along withcatalysts. Suitable hardeners are those commonly used, for examplesorganic peroxides such as diacyl peroxides, e.g. benzoyl and lauroylperoxide; ketone peroxides e.g. acetone and cyclohexanone peroxides;hydrocarbon peroxides, e.g. tert-butyl, cumyl, decahydronaphthylperoxides; dihydrocarbyl peroxides e.g. di-tert-butyl and dicumylperoxides; percetals e.g.1,1-di-tert-butylperoxy-3,3,5-trimethylcyclohexane; peresters e.g.tert-butylperbenzoate, tert-butylperoxyisopropyl-percarbonate,bis(4-tert-butylcyclohexyl) peroxydicarbonate, butyl and cyclohexylpercarbonate, bicyclohexyl peroxydicarbonate, tert-butyl perpivalate,tert-butyl peroctoate and tert-butyl permaleate; as well asacetylcyclohexane sulfonyl peroxide. Usual azoic initiators, such asazobisisobutyronitrile, and conventional primary and secondary aliphaticor aromatic amines, e.g. diethylenetriamine, are suitable as well. Theboron trifluoride monoethylamine complex may also be used as hardener.Anhydrides, such as hexahydrophthalic acid anhydride, are alsoappropriate; in the case of hexahydrophthalic acid anhydride,N-benzyldimethylamine is advantageously used as catalyst. Halogenatedantimony, e.b. SbF₆, may also be used. The type of hardeners dependsupon the functionality to be polymerised. If the functionality is adouble bond C═C, the hardener is usually a peroxy compound. If thefunctionality is an epoxy, the hardener is an amine, SbF₆,hexahydrophthalic acid anhydride/N-benzyldimethylamine, or borontrifluoride monoethylamine complex. For the curing of epoxy, preferredhardeners are anhydride/amine and boron trifluoride. The amount ofhardener may range widely; in case of epoxy curing it may range from 1to 100%, based on the epoxy content, preferably from 5 to 50%. Whencatalysts are used along with hardeners, they may represent from 0,01 to100 wt % preferably 5%, based on the weight of hardener.

The thermal curing, with or without hardener, is carried out at atemperature comprised 20° and 200° C., preferably 50° and 150° C. Thecuring time may vary widely; usually it is comprised between 10 mn and72 hours, preferably between 0,5 and 20 hours. The thermal curing may becarried out under vacuum, optionally.

The photocuring may be an IR-curing, an UV-curing, or any suitablephotocuring, e.g. a curing acting under actinic radiation, and the like.Preferably, the photocuring is a UV-curing. In this latter case,initiators UV-activated are suitable. Examples of said initiators are:1-hydroxy-cyclohexylphenylketone, benzyldimethylcetal,2-hydroxy-2-methyl-1-propanone, butyl oxide, benzoine oxide, ethyloxide, benzophenone, benzoine, substituted thioxanthones and ionicphotoinitiators like triarylsulfoniumhexafluoro-phosphate and-antimonate salts (e.g. Cyracure UVI 6974 from Union Carbide). Apreferred UV-initiator is 1-hydroxy-cyclohexylphenylketone, for thecuring of (meth)acryloxy functionalities of the group Y of component b).The 1-hydroxy-cyclohexyl-phenylketone is commercially available underthe tradename IRGACURE 184 (Ciba-Geigy company).

The amount of thermal or UV-curing initiator is comprised between 0.01to 5 wt %, based on the weight of the lacquer; it may also be calculatedbased on the content of polymerizable groups, as state hereinabove.Accelerators may also be added to the foregoing. Examples of suchaccelerators are tertiary amines, preferably N-methyldiethanolamine. Theamount of said accelerator is comprised between 10 and 300 wt %,preferably 50 and 200 wt %, based on the weight of the photoinitiator.

According to an embodiment of the present invention, the curing isalternately thermal and a UV-curing. Different sequences have been foundto be efficient. Examples are given below, wherein p means photocuringwith Irgacur under UV radiations; and t means thermal curing at 120° C.with anhydride/amine or boron trifluoride. The number betweenparentheses after t and p stands for the curing time, expressed in hoursand minutes, respectively. These examples are given by way ofillustration of combining t and p-curing: p(1)-t(16); t(16)-p(1);t(1)-p(1)-t(16); and the like.

According to another embodiment, the curing can be a two-step curing, inthat sense that a photocuring is first carried out, so as to enable thecoated substrate to be handled, and a thermal curing is then carried outto completely cure the lacquer. The first step is quite short, e.g.about 30 seconds, and the coating becomes non-sticky, so that thethus-coated substrate can be easily handled. The lacquer, at this time,is a "precured" lacquer. The second step requires a longer period oftime, e.g. 16 hours. Due to the fact, the substrate is non-sticky, thereis no requirement of a minimal distance between the substrates places inthe oven: there is no risk of sticking together. This embodiment allowseasier and faster processing, smaller ovens, and the like.

The coating obtained by the present process has a thickness comprisedbetween 0.1 and 200 μm, preferably between 1 and 150 μm. Before applyingthe lacquer, the substrate may be coated with a keying agent or with aprimary layer or sub-layer, although this pre-coating is not required.The coating may also be obtained as a dual layer, the sub-layer beinge.g. a lacquer with a filler and the external layer being a purelacquer.

Any substrate may be coated with the present lacquer, and particularlysubstrates such as SMDs and PCBs. The substrate can for example be athin-film capacitor, multiplechip module, resistor, integrated circuit,Si-wafer, optical component. The present lacquers show a very highadhesion on these various substrates, being adherent to metal,polyester, ceramics, and the like.

Thus, another object of the present invention is to provide substrateshaving applied thereon a coating obtained by the present process. Also,the present coating process may alternatively be expressed as the use ofthe present lacquer as a coating.

The present invention is now described in more details in the followingexamples, which have to be understood as illustrative of the scope ofthe invention and in no case as limiting said scope, defined in theappended claims.

EXAMPLE 1

Synthesis of GMP2Zr

The preparation of system GMP2Zr is described for a 0.4 mol formulation:

    ______________________________________                                        94.45 g                                                                              (0.4 mol, 38.6 mol %)                                                                         GLYMO (3-glycidyloxypropyl-                                                   trimethoxysilane from the                                                     company Union Carbide)                                 99.24 g                                                                              (0.4 mol, 38.6 mol %)                                                                         MEMO (3-methacryloxypropyl-                                                   trimethoxysilane from the                                                     company Fluka)                                         41.97 g                                                                              (0.2 mol, 18.92 mol %)                                                                        diphenylsilanediol (from the                                                  company Fluka)                                         13.10 g                                                                              (0.04 mol, 3.86 mol %)                                                                        Zr (tetraisopropoxyzirconate                                                  from the company Fluka)                                ______________________________________                                    

Into a 500 ml three-necked glass flask equipped with a multiple coilcondenser, a thermometer and a drop funnel the monomers are weighed inthe sequence given above. The suspension is stirred magnetically and thetemperature will decrease by about 1°-2° C. The suspension becomes aviscous paste. After about 30 min, the reaction temperature willincrease slightly, but after 5 hours the exothermic hydrolysis reactionstarts and leads to a clearing of the mixture. At this time thetemperature may rise over 25° C., and the mixture is then cooled down to20° to 23° C. using a water bath. The reaction mixture needs 13additionnal hours of stirring at room temperature for a completeconversion.

After storage of two days at 20° C. (climatized chamber) the GMP2Tlacquer is fit for application. At that time the inherent viscosity isabout 12 mm² /s (determined by an Ubbelohde capillary viscosimeter at20° C.).

EXAMPLE 2

In 10 g of the GMP2Zr lacquer as prepared above, 1.22 g ofhexahydrophthalic acid anhydride (50 mol% based on the epoxy content)and 0.061 g of N-benzyldimethylamine (5 wt % based on the acidanhydride) are added. Thin-film PET capacitors (C₀ =450 nF) are dippedin this solution. A spin-off process (600 rpm for 40 sec) follows.Curing of the coating is performed by heating at 120° C. for 16 h. Theapplied coating has a thickness of about 4 μm. Testing of thethus-coated capacitors under humid conditions (90° C., relative humidityRH: 100%) shows a start of decrease in capacitance after 5 days whereasfor the uncoated ones the decrease starts after only 1 day. A workablecapacitor should withstand the foregoing humid conditions for 3 daysbefore capacitance decrease starts in order to be acceptable as an SMD.The test is performed with two sets of 20 capacitors.

EXAMPLE 3

In 10 g of the GMP2Zr lacquer as prepared above, 1.22 g ofhexahydrophthalic acid anhydride (50 mol % based on the epoxy content)and 0.061 g of N-benzyldimethylamine (5 wt % based on the acidanhydride) are added. Thin-film PEN capacitors made of 2 μm thin-films(100 nF) are dipped in this solution. Curing of the coating is performedby heating at 120° C. for 12 h. The applied coating has a thickness ofabout 5 μm. An accelerated life test at 90° C. and 100% RH is chosen toquickly observe differences between the coated and uncoated components.No voltage is applied. The criterion used for comparison was the timethat components withstand these conditions with a net relativecapacitance shift of less than 5%. The result is given in FIG. 1. Theuncoated chips reach -5% rapidly within 2 days; but for coated chipseven after 30 days under test conditions, only 60% of the totalelectrode area has been eroded.

EXAMPLE 4

Synthesis of GMP2ZrHydr

The preparation of system GMP2ZrHydr is described for a 0.4 molformulation:

    ______________________________________                                        94.45 g                                                                              (0.4 mol, 38.6 mol %)                                                                         GLYMO (3-glycidyloxypropyl-                                                   trimethoxysilane from the                                                     company Union Carbide)                                 99.24 g                                                                              (0.4 mol, 38.6 mol %)                                                                         MEMO (3-methacryloxypropyl-                                                   trimethoxysilane from the                                                     company Fluka)                                         41.97 g                                                                              (0.2 mol, 18.92 mol %)                                                                        diphenylsilanediol (from the                                                  company Fluka)                                         13.10 g                                                                              (0.04 mol, 3.86 mol %)                                                                        Zr (tetraisopropoxyzirconate                                                  from the company Fluka)                                10.65 g                                                                              (0.59 mol, 25% stoich)                                                                        H.sub.2 O                                              ______________________________________                                    

Into a 500 ml-three-necked glass flask equipped with a multiple coilcondenser, a thermometer and a drop funnel the monomers are weighed inthe sequence given above. The suspension is stirred magnetically and thetemperature decreases by about 1°-2° C. The stirring at room temperatureis stopped after 18 h. Then the temperature is brought to about 70° C.within a period of time of about 90 min. The composition becomes clearand the total amount of water is added in a single step. The temperatureof the mixture is maintained at about 70° C. When the lacquer becomesclear after the addition of water (about 20-30 min), the composition isstirred for a further hour while being kept heated. After completion ofthe reaction, the lacquer cools down to room temperature.

PROPERTIES

Some of the properties the new lacquer is endowed with are given below.

Good adhesion to substrate:

The present coating shows good adhesion to various substrates. Theadhesion is measured with cross-cut tape test for coatings 10 μm thickaccording to the method DIN 53151. The scale ranges from 0 to 5; forexample, the adhesion on flat glass, Al, stainless steel is comprisedwithin the respectives ranges of: 0.5-1.5; 1.5-2.5 and 0-1. Further, thecoating wets PET and PEN, the polyester constituting thin-filmcapacitors with wetting angles less than 20°.

Thermal stability:

The coating has been applied to Al and heated in steps of 1 hour at 150°C., 180° C., 210° C., 240° C., 270° C. and 300° C. No crack formation orcolor change appears until up to the highest temperature. A particularimmersion for 30 sec in a bath of molten solder at 280° C. does notaffect the material properties.

Electrical properties:

The breakdown strength is about 200 V/μm, as measured on nickel; thedielectric constant (ε at 1 kHz) is about 4.

Contaminants:

The present coating has a very low alkali content (as low as 10 ppm).The presence of contaminants being one factor that contributes toelectrode erosion and corrosion, the present coatings are lesssusceptible to corrosion.

Chemicals:

The present coating is resistant to commonly used industrial solventsand detergents.

Behavior towards water:

The water absorption is less than 0.5% and the water vapor permeationrate (WVPR) is about 15 g/m² d, as measured for a 100 μm thick coating.Water is an important factor making for corrosion and the low WVPR ofthe present coating thus reduces corrosion.

Long shelf-life:

Shelf-lives of more than 200 days are obtainable. This is an advantagecompared to conventional epoxy systems which need to be procesed withina short period of time after completion of the reaction.

Viscosity:

Component miniaturisation requires that coatings applied to the chipshould be very thin, typically less than 100 μm. Possible applicationtechnologies for capacitors include dip-coating (eventually followed byspinning off excess material), screen-printing or coating of thecut-edges by a dip process similar to the one used to apply theconducting paste as electrodes on ceramic chips. Different technologiesrequire different viscosities of the starting material. The viscosity ofthe present lacquer can easily be adapted to these requirements.

We claim:
 1. A process for making a lacquer comprising the steps of:(i)precondensing:a) 1 to 10 mol % of at least one zirconium compound of theformula I:

    ZrR.sub.4                                                  (I)

wherein:R is halogen, hydroxy, alkoxy, acyloxy or chelated ligand; b) 20to 94 mol% of at least one organic silane of the formula II:

    R".sub.m (R"'Y).sub.n SiX.sub.(4-m-n)                      (II)

wherein: R" is alkyl, alkenyl, aryl, alkylaryl, arylalkyl, alkenylaryl,or arylalkenyl; R"' is alkylene, alkenylene, arylene, alkylarylene,aryl-alkylene, alkenyl-arylene, or arylalkenylene; R" and R"' beingoptionally interrupted by oxygen, sulfur or --NH--; X is hydrogen,halogen, hydroxy, alkoxy, acyloxy, or --NR'₂ where R' is hydrogen oralkyl; Y is a polymerizable group; m is an integer from 0 to 3 and n isan integer from 1 to 3; m+n is from 1 to 3; and c) 5 to 30 mol% of atleast one organic silane of formula III:

    R".sub.p SiX.sub.4-p                                       (III)

wherein R" and X are defined in b), and p is 1, 2 or 3; and d) 0 to 10mol% of at least one low-volatility metal oxide, soluble in theprecondensation reaction medium, of an element of groups Ia to Va or IVbor Vb of the Periodic Table of the Elements, or a compound of one ofthese elements, soluble in the reaction medium, forming a low-volatilityoxide;optionally in the presence of an organic solvent at a temperatureof between 10 and 80° C. for a period of time ranging from between 0.5and 72 hours; and ii) condensation the precondensate of step (i) withoutwater or with up to 50% of the stoichiometric amount of water, at atemperature of between 20 and 90° C. for a period of time from between0.5 and 72 hours.
 2. The process according to claim 1 wherein theprecondensation of step (i) is carried out in the absence of water. 3.The process according to claim 1 wherein the component a) of formula Irepresents from 2 to 6 mol%, the component b) of formula II represents69 to 83 mol%, the component c) of formula III represents 15 to 25 mol%,and the component d) represents 0 mol%.
 4. The process according toclaim 1 wherein component a) of formula I is Zr(O-isoC₃ H₇)₄.
 5. Theprocess according to claim 1 wherein at least one component b) offormula II is (R"'Y)SiX₃, wherein R"' is a C₁₋₄ alkylene, Y is acryloxy,methacryloxy, glycidyloxy, allyl, vinyl, or epoxycyclohexyl, and X isC₁₋₄ alkoxy.
 6. The process according to claim 1 wherein component b) offormula II is 3-glycidyloxypropyltrimethoxysilane and/or3-methacryloxypropyltrimethoxysilane.
 7. The process according to claim1 wherein component c) of formula III is R"₂ SiX₂, wherein R" is an aryland X is hydroxy or C₁₋₄ alkoxy.
 8. The process according to claim 7wherein component c) is (C₆ H₅)₂ Si(OH)₂.
 9. The process according toclaim 1 wherein component a) is Zr(O-isoC₃ H₇)₄ ; component b) is (R"'Y)SiX₃, wherein R"' is a C₁₋₄ alkylene, Y is acryloxy, methacryloxy,glycidyloxy, allyl, vinyl, or epoxycyclohexyl, and X is C₁₋₄ alkoxy; andcomponent c) is R"₂ SiX₂, wherein R" is aryl and X is hydroxy or C₁₋₄alkoxy.
 10. The process according to claim 1 wherein the condensation ofstep (ii) is carried out in the absence of water.
 11. The processaccording to claim 1 wherein the precondensation step (i) is carried outin the absence of external solvent.
 12. The process according to claim 1in which the precondensation of step (i) and/or the condensation of step(ii) is carried out catalytically.
 13. The process according to claim 1wherein the precondensation of step (i) is carried out at a temperatureof between 15° and 50° C. and for a period of time ranging from 1 to 48hours.
 14. The process according to claim 1 wherein the condensation ofstep (ii) is carried out at a temperature of between 25° and 700° C. andfor a period of time ranging from between 2 and 48 hours.
 15. Theprocess according to claim 1 wherein the lacquer made by the process hasan inherent viscosity ranging from between 5 and 1000 mm² / second. 16.The process according to claim 1 which further comprises step (iii)adding additional additives to the precondensate (i) and/or thecondensate (ii).
 17. The process according to claim 16 wherein theadditional additives are fillers added in an amount ranging from 1 to70%, based on the weight of the lacquer.
 18. A lacquer obtained by aprocess comprising the steps of:(i) precondensing:a) 1 to 10 mol% of atleast one zirconium compound of the formula I:

    ZrR.sub.4                                                  (I)

wherein:R is halogen, hydroxy, alkoxy, acyloxy or chelated ligand; b) 20to 94 mol% of at least one organic silane of the formula II:

    R".sub.m (R"'Y).sub.n SiX.sub.(4-m-n)                      (II)

wherein:R" is alkyl, alkenyl, aryl, alkylaryl, arylalkyl, alkenylaryl,or arylalkenyl; R"' is alkylene, alkenylene, arylene, alkylarylene,aryl-alkylene, alkenyl-arylene, or arylalkenylene; R" and R"' beingoptionally interrupted by oxygen, sulfur or --NH--; X is hydrogen,halogen, hydroxy, alkoxy, acyloxy, or --NR'₂ where R' is hydrogen oralkyl; Y is a polymerizable group; m is an integer from 0 to 3 and n isan integer from 1 to 3; m+n is from 1 to 3; and c) 5 to 30 mol% of atleast one organic silane of formula III:

    R".sub.p SiX.sub.4-p                                       (III)

wherein R" and X are defined in b), and p is 1, 2 or 3; and d) 0 to 10mol% of at least one low-volatility metal oxide, soluble in theprecondensation reaction medium, of an element of groups Ia to Va or IVbor Vb of the Periodic Table of the Elements, or a compound of one ofthese elements, soluble in the reaction medium, forming a low-volatilityoxide;optionally in the presence of an organic solvent at a temperatureof between 10° and 80° C. for a period of time ranging from between 0.5and 72 hours; and ii) condensation the precondensate of step (i) withoutwater or with up to 50% of the stoichiometric amount of water, at atemperature of between 20° and 90° C. for a period of time from between0.5 and 72 hours.
 19. The lacquer according to claim 18 wherein theprecondensation of step (i) occurs in the absence of water.
 20. Thelacquer according to claim 18 wherein the component a) of formula Irepresents from 2 to 6 mol%, the component b) of formula II represents69 to 83 mol%, the component c) of formula III represents 15 to 25 mol%,and the component d) represents 0 mol%.
 21. The lacquer according toclaim 18 wherein component a) of formula I is Zr(O-isoC₃ H₇)₄.
 22. Thelacquer according to claim 18 wherein at least one component b) offormula II is (R"'Y)SiX₃, wherein R"' is a C₁₋₄ alkylene, Y is acryloxy,methacryloxy, glycidyloxy, allyl, vinyl, or epoxycyclohexyl, and X isC₁₋₄ alkoxy.
 23. The lacquer according to claim 18 wherein component b)of formula II is 3-glycidyloxypropyltrimethoxysilane and/or3-methacryloxypropyltrimethoxysilane.
 24. The lacquer according to claim18 wherein component c) of formula III is R"₂ SiX₂, wherein R" is aryland X is hydroxy or C₁₋₄ alkoxy.
 25. The lacquer according to claim 24wherein component c) is (C₆ H₅)₂ Si(OH)₂.
 26. The lacquer according toclaim 18 wherein component a) is Zr(O-isoC₃ H₇)₄ ; component b) is(R"'Y)SiX₃, wherein R"' is a C₁₋₄ alkylene, Y is acryloxy, methacryloxy,glycidyloxy, allyl, vinyl, epoxycyclohexyl, and X is C₁₋₄ alkoxy; andcomponent c) is R"₂ SiX₂, wherein R" is aryl and X is hydroxy or C₁₋₄alkoxy.
 27. The lacquer according to claim 18 wherein the condensationof step (ii) is carried out in the absence of water.
 28. The lacqueraccording to claim 18 wherein the precondensation step (i) is carriedout in the absence of external solvent.
 29. The lacquer according toclaim 18 in which the precondensation of step (i) and/or thecondensation of step (ii) is carried out catalytically.
 30. The lacqueraccording to claim 18 wherein the precondensation is carried out at atemperature of between 15° and 50° C. and for a period of time rangingfrom 1 to 48 hours.
 31. The lacquer according to claim 18 wherein thecondensation of step (ii) is carried out at a temperature of between 25°and 70° C. and for a period of time ranging from between 2 and 48 hours.32. The lacquer according to claim 18 wherein the lacquer has aninherent viscosity ranging from between 5 and 1000 mm² /second.
 33. Thelacquer according to claim 18 wherein the lacquer contains additionaladditives.
 34. The lacquer according to claim 33 wherein the lacquercontains from 1 to 70% of fillers, based on the weight of the lacquer.35. The lacquer according to claim 18 which is free of solvent.
 36. Aprocess for coating a substrate which comprises the steps of applying ona surface of said substrate the lacquer of claim 18 and curing thelacquer.
 37. The process according to claim 36 wherein the curing is athermal curing, carried out at a temperature ranging from between 20°and 200° C., for a period of time ranging from between 10 minutes and 72hours.
 38. The process according to claim 36 wherein the curing iscarried out in the presence of hardeners.
 39. The process according toclaim 36 wherein the curing is photocuring, carried out in the presenceof a photoinitiator for a period of time ranging from between 2 secondsand 10 minutes.
 40. The process according to claim 36 wherein the curingis a thermal and a photocuring.
 41. The process according to claim 36wherein the curing is comprised of steps of photocuring followed bythermal curing.
 42. The process according to claim 36 in which thelacquer is applied through the steps of dip-coating the substrate in thelacquer and spinning-off lacquer from the substrate.
 43. The processaccording to claim 36 wherein the thickness of the coating ranges frombetween 0.1 and 200 microns.
 44. The process according to claim 43wherein the thickness of the coating ranges from between 1 and 150microns.
 45. A substrate comprising at least one surface having acoating applied thereon, the coating comprising the lacquer of claim 18.46. The substrate according to claim 45 which is a surface mounteddevice.
 47. The substrate according to claim 45 which is mounted on aprinted circuit board.
 48. The substrate according to claim 45 which isa thin film capacitor.
 49. The substrate according to claim 45 which isa multiple chip module.
 50. The substrate according to claim 45 which isan optical component.
 51. The substrate according to claim 45 which is aresistor.
 52. The substrate according to claim 45 which is an integratedcircuit, optionally encapsulated.
 53. The substrate according to claim45 which is a silicon-wafer.
 54. The substrate according to claim 48which is a printed circuit board.
 55. The method of coating whichcomprises coating the laquer of claim 18 onto a thin film capacitor.